Young dependent adult question please

Hello,

Hope all is well. Would appreciate the advice on the following matter:

1) I'm residing in the State for almost 5 years now, and plan to apply for citizenship later this year.
2) Last year, I brought a son from my first marriage. Back then he was 17, now 18, and going to school.
3) He entered the State legally, as a part of the family unit 1 year and 1 month ago.

My questions are:

1) To be eligible to apply for citizenship as a dependent young adult, how many years he must possess?
2) As far as I can understand, he could use my years of reckonable residence. Is this true?
3) If he wouldn't be able to use my years of experience, the only way to keep going is to enter into the Third Level Education?

Thanks in advance!